Polyphenylene ethers (or oxides) are known and described in numerous publications including U.S. Pat. Nos. 3,306,874 and 3,306,875 of Allan S. Hay and U.S. Pat. Nos. 3,257,357 and 3,257,358 of Gelu Stamatoff. The high molecular weight polymers are high performance engineering thermoplastics possessing relatively high melt viscosities and softening points--i.e., in excess of 275.degree. C.--and are useful alone and in combination with other polymers--for many commercial applications requiring high temperature resistance including formation of film, fiber and molded articles.
These polymers may be produced by the oxidative coupling of suitable phenolic monomers. This may be accomplished utilizing oxygen and a catalyst such as copper-amine complex, or by a catalyst such as manganese bis(benzoin oxime) in a basic reaction medium.
One such process for producing these polymers involves polymerization in a biphasic system. Two immiscible liquid phases are involved. One is normally aqueous; the other, aromatic organic. Oxygen, oxidative catalyst, monomer and any desired additional ingredients are dispersed in the basic system, with individual ingredients being preferentially disposed in one or the other of the phases. In an alternative process, a single phase system is employed. In both such processes the polymerization reaction proceeds exothermically, usually under some agitation of the system.
Upon completion of the polymerization reaction, the polyphenylene ether polymer is isolated from the reaction medium. This may be accomplished by various known means. For example, a water soluble organic liquid such as methanol or acetone may be added to the reaction medium or steam may be injected into that medium. In either instance, the polymer precipitates and is readily separated from the supernatant liquid medium.
Another common step in the production of polyphenylene ether involves decolorization. This step may be accomplished by catalytic hydrogenation of the polymer. Alternatively or additionally, the polymer may be decolorized by passing the solution through a column packed with alumina or other suitable adsorbant to remove the colored impurities. Similarly, a reducing agent such as hypophosphorous acid may be employed for decolorization. Decolorization is ordinarily performed prior to isolation and while the polymer is still dissolved in the reaction medium. It results in polymer compositions having a more desirable appearance.
While the high performance properties of polyphenylene ethers are most desirable, their relatively high melt viscosities and softening points are often a disadvantage. For example, although they may be employed to produce superior molded articles by melt processing techniques, the high temperatures required are undesirable.
Because of this disadvantage, polyphenylene ethers are often combined with other resins for commercial use. One such resultant class of compound compositions is described in U.S. Pat. No. 3,383,435 of Eric P. Cizek. Those compositions, containing polyphenylene ether (or oxide) in admixture with polyalkenyl aromatic resin are generally employed in the production of molded and/or extruded articles.
It is known in the art that various of the properties of these compound compositions may be further improved by copolymerizing the alkenyl aromatics with other monomers or by blending with other resins. Modifiers such as butadiene, for example, are customarily incorporated into the polyalkenyl aromatic resins to improve the properties of the resultant compositions. Such modified resins provide means for overcoming various physical drawbacks of alkenyl aromatic resins, particularly polystyrene, while simultaneously facilitating the processing of polyphenylene ethers.
As is described in the art, butadiene modification of polyalkenyl aromatic resins may take many forms. Polybutadiene or copolymers partially derived from butadiene may be graft, block or otherwise polymerized with such alkenyl aromatic resins. The resultant product may also be unsaturated or saturated (for example, by subsequent hydrogenation) without loss of desirability.
Despite the foregoing hydrogenation step and compounding with other polymers, polyphenylene ether compositions often exhibit undesirable color and/or color stability. This may lead to loss of consumer acceptability or to dissatisfaction with appearance. As a result, polyphenylene ether compositions having improved color properties remain highly desirable.